But some evidence to support that rumor has popped up recently. Just last month, Apple released a new beta version of iOS 7 thatcontained a folder labeled Biometric Kit that had references for tools developers could use to take advantage of a fingerprint sensor on future hardware.

How fingerprint sensors work

Humans have small ridges on their fingers. Fingerprint sensors try to make a map of those ridges, and look for patterns like loops, arches, and spirals, smart key startup KeyMe CTO Kris Borer tells Business Insider.

We've heard rumors that the sensor would be embedded into the home button. In the years to come, there's also been talk that future iPhones and iPads could have fingerprint sensors embedded in the touchscreen.

If Apple does integrate fingerprint sensors into its next iPhone, developers would have one more option for verifying who someone is, Borer says. The technology could potentially be used for a secure login, device sharing, payments, and any other application where the identity is relevant.

But it will likely break after a little while, given the poor durability of the actual surface, Parziale writes. Even though Apple could use it for payments, it may not be a good idea.

Sweat, dirty pockets, hot and cold environments, sun exposure, and other factors can affect the sensitivity and working conditions of the sensor surface.

"And if they do [use it for payments], they are making a huge mistake, because the surface destruction process... introduces the most dangerous problem in fingerprint recognition: false acceptance, when after a while somebody else can be granted access to your device," Parziale writes.

Security and other issues

It's possible that two people could have very similar fingerprints, Borer says. The technology is also more difficult to work with than passwords and security questions. Fingerprints take up more space, which requires more network bandwidth.

"They also require more processing and more complicated algorithms to match," Borer says. "That said, with fingerprints you do not have to remember anything, and it is much harder to steal a fingerprint than a password."

Why fingerprint technology has failed in handheld devices in the past

Companies like Motorola, Fujitsu, Siemens, and Samsung have tried to integrate fingerprint technology into mobile devices and even PCs. But their efforts ultimately failed because of the sensor surface deteriorating over time.